1. Field of the Invention
The present invention generally relates to a liquid crystal display device, and more particularly, a liquid crystal display device having spacers with uniform height to maintain the uniform and precise cell gap between the two glass substrates of liquid crystal display device.
2. Description of the Related Art
A liquid crystal display device typically includes a pair of substrates which are maintained in a space apart, yet parallel relationship with one another. The space between the substrates is commonly referred to as the cell gap. Interposed between the substrates, within the cell gap, is a liquid crystal material which changes its optical characteristics in response to an applied electrical signal.
A plurality of electrodes are disposed upon the inner surface of the substrates in order to control and apply the desired electrical signals to the liquid crystal material. Some LCD devices will have an electrode arrangement which allows a predetermined set of characters or symbols to be generated, while other LCD devices have a matrix of electrodes that form a display comprised of a great plurality of individually accessible pixel elements, each of which may be selectively activated to form an infinite variety of images.
Due to the electro-optical characteristics inherent in the liquid crystal material, its state varies with the application of an electrical signal state varies. For example, some liquid crystal materials will assume a reflective state when no electrical signal is applied, and will assume a transmissive state under the influence of an applied electrical signal. Some new liquid crystal materials perform with a variety of different gray levels as well.
In order to assure the proper operation of a liquid crystal display device, it is critical that the cell gap is maintained uniformly and precisely throughout the entire display. Even slight deviations in the cell gap will result in a noticeable and defective appearance in the display (so-called Mura defect). This can readily be seen in a conventional LCD display panel with a fingertip pressure on the surface. In response to the pressure, the cell gap in the affected area will be reduced slightly, resulting in a dark spot, degradation of contrast or other undesirable defects in the displayed image.
In a conventional technology, the LCD device includes a TFT substrate, a color filter substrate and liquid crystal material sandwiched therebetween. The cell gap is maintained by providing a plurality of spacers between the substrates. The spacers, which are of a uniform height, are disposed randomly within the cell gap, by virtue of a spraying technique. This generally results in an uneven distribution of spacers. To ensure that an adequate concentration of spacers to maintain the proper cell gap is disposed in all areas of the display, a superfluity of spacers must be used. In addition, according to such conventional techniques for placement of the spacers, they are placed in both xe2x80x9cinactivexe2x80x9d and xe2x80x9cactivexe2x80x9d areas of the display. The xe2x80x9cactivexe2x80x9d areas are those areas where the liquid crystal material may be selectively activated because they are located between opposed electrodes upon the substrates. The xe2x80x9cinactivexe2x80x9d areas are those areas where the liquid crystal material cannot be selectively activated because of the absence of opposed electrodes on the substrates.
Inherently, there are several undesirable deficiencies in the structure and performance of the liquid crystal display panel existing in such conventional spacer techniques. Spacers which are disposed in the active display areas, particularly due to the superfluity of spacers, cause defects, such as the degradation of contrast or the undesirable emission of light around the edges of the spacers therein.
Therefore, European Patent 1030211 A2, incorporated herein by reference, discloses a liquid crystal display, which can omit the step of scattering spacers and thus avoiding deviations in cell thickness due to the uneven distribution of spacers. This LCD generally includes a TFT (Thin Film Transistor) substrate, a CF (Color Filter) substrate and a liquid crystal material layer sealed therebetween. The projection patterns formed on the CF substrate have a height of about 4.0 xcexcm to keep the uniform cell gap. However, it is necessary to form the projection patterns by extra processes of applying, exposing and developing a photoresist disposed on the electrode layer, which may cause the substantial increase in cost.
U.S. Pat. No. 5,757,451 entitled xe2x80x9cLiquid Crystal Display Device Spacers Formed From Stacked Color Layersxe2x80x9d issued on May 26, 1998 to Miyazaki et al., incorporated herein by reference, discloses a pillar-shaped spacer disposed by stacking of a plurality of different color filter layers on a substrate of the LCD device for keeping a cell gap thereof. Also, U.S. Pat. No. 6,147,729 entitled xe2x80x9cLCD Having Stacked Color Filter Spacers In Which Some Spacers Are Continuous With A Color Filter Layer And Others Are Notxe2x80x9d issued on Nov. 14, 2000 to Kurauchi et al., incorporated herein by reference, discloses another stacked color filter spacers for keeping a cell gap of a LCD device.
However, the spacers as mentioned above still have some problems. First, the spacers shown in FIG. 1 are formed in such a manner that the uppermost layer 18c of the spacer portion and the colored layer 14c on the pixel area are continuous, i.e., it is difficult to control the width W and the height h of the spacer portion of the space 19c. Since the increase of the width W may cause the spacer portion to enter into the pixel region, the open ration will be reduced, and the uneven cell gap may be created due to variation in the height h of the spacer.
Furthermore, referring to FIGS. 2 to 4, they depict a variety of the stacked color filter spacers. The spacers shown in FIGS. 2a, 2b and 4a, 4b, which are formed by stacked color filters 22, 23 are in the shape of a pillar and a rectangle, respectively. However, the color filter is formed on the substrate of the LCD device by the process of applying, exposing and developing a color filter resin disposed on the substrate. The uppermost color filter 22 may not be precisely positioned with respect to the lower color filter 23 due to misaligning in the above mentioned process, and then flows down in the sequent process of high temperature, so the height of the spacer is varied, as shown in FIGS. 3a, 3b and 5a, 5b, thereby causing the uneven cell gap and generating the Mura defect.
Accordingly, there exist needs for providing a liquid crystal display device having spacers with uniform height to maintain the uniform and precise cell gap between the two glass substrates of liquid crystal display device in order to substantially reduce the Mura defect.
It is a primary object of the present invention to provide a liquid crystal display device having spacers with uniform height to maintain the uniform and precise cell gap between the two glass substrates of liquid crystal display device so as to substantially reduce the Mura defect.
In order to achieve the objects mentioned hereinabove, the present invention provides a color filter substrate for a LCD device. The color filter substrate comprises a transparent substrate having a substantially flat surface, a black matrix, a plurality of color filters, an electrode, a plurality of spacers, and an alignment film. The black matrix is formed on predetermined regions of the substrate. The color filter portion having colored layers of plural colors disposed on the transparent substrate. The plurality of spacers each having a first spacer member and a second spacer member, wherein the first spacer member and the second spacer member are formed by different layers both in the shape of a parallel construction, and overlap and intersect at a predetermined angle such that each of the spacers has an uniform height.
In one embodiment of the invention, the first spacer member and second spacer member are formed by different color layers, and the electrode is formed over the black matrix, the color filters and the spacers.
In another embodiment of the invention for MVA LCD, the color filter substrate further comprises domain regulating means, such as protrusion patterns, and the first spacer member is formed by a color layer and the second spacer is formed by a part of protrusion patterns. The electrode is formed over first spacer member and under protrusion patterns.
In another aspect according to the present invention, there is provided a color filter substrate wherein the predetermined angle is 90 degree.
In further aspect according to the present invention, there is provided a color filter substrate wherein the parallel construction is a rectangle and a parallelogram.
In still further aspect according to the present invention, there is provided a color filter substrate wherein the spacers are positioned on the regions of the black matrix.
In still further aspect according to the present invention, there is provided a color filter substrate wherein the spacers are positioned on the regions opposite to the storage capacitors on TFT substrate.
In the process of forming the spacers., the alignment accuracy between mask and glass substrate has a great influence on the alignment of two spacer members. In general, the aligner for photo-resist expose process comes across two types of misalignment between photomask and color filter glass. One is occurring in parallel shift and the other is happening in rotating movement. The margin error of parallel shift is within the range of xc2x13 xcexcm and the rotation is almost 0 degree, so there is almost no rotational misalignment. The parallel misalignment has no effect on the height of the intersected portions of two parallel constructions according to the present invention. Therefore, the spacers are uniform in the overall glass substrate, thereby substantially reducing the Mura defect mainly due to irregular cell gap.